As the miniaturization of mobile communication terminals, particularly mobile telephones, increases, antennas with smaller and smaller dimensions will be needed in the future. In the field of mobile telephones, therefore, so-called “stub antennas,” which only protrude out of the casing for a short distance, have mainly been used in recent times. These “stub antennas” have the disadvantage that they are mechanically sensitive and can break off. In addition, the antennas should also disappear visually as completely as possible in the miniaturized casing for design reasons. One possibility of completely integrating antennas consists in using antennas of the type mentioned initially, with a printed conductor pattern applied in or to a support; for example, so-called “PCB (printed circuit board) antennas”.
Such an integrated antenna must be capable of covering the entire bandwidth of the respective radio channel. In the so-called 900-MHz GSM band, for example, transmission is in the range from 880 to 915 MHz and reception is in the range from 925 to 960 MHz so that the antenna must properly cover the range from 880 to 960 MHz. To this is added the problem, particularly in the case of mobile telephones, that the antenna resonance can shift to a different degree during the talk time which is caused by the different positions of the mobile radios in the hand of the user. This shift in the resonant frequency correspondingly must be compensated for by the antenna having an even wider bandwidth than the frequency band needed so that the entire band can be operated in even with a shift in the resonant frequency. However, wide band antennas are usually obtained if they are geometrically large, which runs counter to the aim of a miniaturized antenna. For example, an ideal antenna would have an effective length of a multiple of a quarter wavelength (λ/4) of the center frequency, of 920 MHz in the case of the 900-MHz GSM band. However, this length often cannot be achieved due to the space provided in the casing.
It is an object of the present invention, therefore, to create an antenna having a relatively wide bandwidth which can be manufactured inexpensively and reproducibly.